We have performed a density functional study on the reaction of C-60 fullerene with one to six 2,3-dimethylbutadiene (DMB) molecule(s) which has previously been investigated by experimental researchers. Based on the obtained results, it has been found that (1) the reaction is regioselective, so that the DMB molecule prefers to be adsorbed atop a C-C bond which is shared between two hexagonal rings of C-60 (in good agreement with the experimental results) with reaction energy of -0.98 eV; (2) the HOMO of DMB interacts with the LUMO of C-60 via a Diels Alder reaction; (3) the energy of reaction and work function of C-60 are decreased by increasing the number of adsorbed DMB molecules; (4) the HOMO-LUMO energy gap of C-60 is slightly changed upon the reaction; (5) the reaction reduces the potential barrier of the field electron emission of C-60 surface. (C) 2012 Elsevier B.V. All rights reserved.